An ideal blood glucose concentration level sensor capable of automatically directing or controlling the operation of an insulin infusion pump should be preferably in the form of a relative small assembly which may be easily implanted in a patient's body and which would be effective in operation and reliable over a long period of time.
Various prior art practioners have sought to provide a medically and commercially device, but there remains further room for improvement. As an example of this prior practice U.S. Pat. No. 4,679,562 Luksha discloses a glucose sensor which provides a detection mechanism adapted to determine glucose levels in blood either in-vivo or in-vitro applications. Enzyme films are described as encased in a silicone rubber film for implantation. Another U.S. Pat. No. 4,650,547 Gough relates to a method and membrane applicable to an implantable sensor. The membrane is disclosed as combination of a hydrophilic material and a hydrophobic material.
U.S. Pat. No. 4,596,575 Rosenberg et al. reveals a liquid delivery system useful as an implantable micropump for delivering insulin or other drugs. Another U.S. Pat. No. 4,557,726 Reinicke shows a pulsatile system and method in which medication is dispensed to the body during short dispensing periods separated by relatively long intervals between such dispensing periods.
U.S. Pat. No. 4,538,616 Rogoff discloses an implantable transducer capable of detecting variations in blood sugar levels by detecting changes in blood osmotic pressure. The transducer operates the insulin and/or glucose pumps which are said to be implanted. Still another U.S. Pat. No. 4,477,314 Richter et al., reveals an electrochemical method for determining glucose in a body fluid.
U.S. Pat. No. 4,366,033 Richter et al. relates to a method for determining the concentration of sugar using an electrocatalytic sugar sensor. A relatively impermeable diaphragm member is used in the process.
Also U.S. Pat. No. 3,837,339 Aisenberg et al. shows an implantable glucose monitor and alarm system for use in the measurement and control of blood glucose levels in diabetics.
Foreign Patent--Germany--DE No. 3228-551-A reveals a method using an electrocatalytic sensor having a measuring electrode fitted with a membrane of measuring glucose in body fluids.
Historically, patients suffering from diabetes have taken the responsibility of controlling their blood sugar level by injections of insulin either on a timely basis or on the basis of symptoms which they feel. Such methods are not exact and only responsive to secondary feelings rather than quantitative body functional measurements. For this reason they are relatively inexact and the control of the disease lacks the kind of controlled medication application which is desired. Consequentially the above patents are examples of the efforts of the medical community has expended to find a more exact and convenient method of providing the appropriate medication such as insulin and/or glucose as the need requires.
As revealed in the prior art patents, the basic components of such a system include a sensing subsystem for the detection of the blood glucose concentration level and another subsystem for providing the appropriate amount of glucose or insulin as needed. The latter subsystem has been developed and components such as pumps, batteries, catheters, and surgical procedures are available, although integrated into relatively complex total system apparatus.
In the sensing subsystem further simplification and increased accuracy in sensitivity are still sought after objectives.
The present invention provides a method and sensor assembly which utilizes as a principle of operation the detection of changes which result from the production of carbon dioxide by yeast in the metabolism of body glucose.